Research Article: Circulating β-endorphin, adrenocorticotrophic hormone and cortisol levels of stallions before and after short road transport: stress effect of different distances

Date Published: March 3, 2008

Publisher: BioMed Central

Author(s): Esterina Fazio, Pietro Medica, Vincenzo Aronica, Loredana Grasso, Adriana Ferlazzo.


Since transport evokes physiological adjustments that include endocrine responses, the objective of this study was to examine the responses of circulating β-endorphin, adrenocorticotrophic hormone (ACTH) and cortisol levels to transport stress in stallions.

Forty-two healthy Thoroughbred and crossbred stallions were studied before and after road transport over distances of 100, 200 and 300 km. Blood samples were collected from the jugular vein: first in a single box immediately before loading (pre-samples), then immediately after transport and unloading on arrival at the breeding stations (post-samples).

An increase in circulating β-endorphin levels after transport of 100 km (P < 0.01), compared to basal values was observed. Circulating ACTH levels showed significant increases after transport of 100 km (P < 0.001) and 200 km (P < 0.001). Circulating cortisol levels showed significant increases after road transport over distances of 100, 200 and 300 km (P < 0.001). An effect of transport on β-endorphin, ACTH and cortisol variations was therefore evident for the different distances studied. No significant differences (P > 0.05) between horses of different ages and different breeds were observed for β-endorphin, ACTH and cortisol levels.

The results obtained for short term transportation of stallions showed a very strong reaction of the adrenocortical system. The lack of response of β-endorphin after transport of 200–300 km and of ACTH after transport of 300 km seems to suggest a soothing effect of negative feedback of ACTH and cortisol levels.

Partial Text

Competitions, breeding, leisure activities, sale or slaughter are the most usual reasons for transporting horses. The necessity of transporting live animals has increased the need to better evaluate horse welfare and health, and thus to verify the effects of transport stress on the variables related to physiological adaptations. Studies to determine the amount of stress experienced by horses during transport have yielded widely varying results. Results are difficult to interpret because transportation involves a range of potential stressors, such as loading, unloading, confinement, vibration, changes in temperature and humidity, inadequate ventilation, space allowed [1] and, frequently, deprivation of food and water. Recently, air stables have proven to be a convenient way of transporting horses on international flights, and caused no discernible ill effects on the horses studied [2]. The effects of long distance transport stress have been widely reported and considered in relation to behavioural [3-5], functional [6-10], endocrine and biochemical variables [11,12], and also in terms of the impact on the immune system [13-15]. The effects of transportation have also been studied with regard to performance [16,17] and reproduction [18,19]. In general, transport by road is more uncomfortable for animals than by rail or air. Moreover, there is ample evidence demonstrating that long periods of road transport have a greater impact on welfare than shorter transport carried out in the same conditions, because of the obvious influence of the prolonged time and the presence of a number of stressors [10,20]. During transport, horses are forced to maintain unnatural body postures for long periods. If this is combined with the additional stress of being placed in an unfamiliar environment, it is likely to have a detrimental effect on the welfare, and even the performance, of some horses [5].

Circulating β-endorphin levels showed an increase (Figure 1) after road transport in Group I (100 Km: P < 0.01), compared to basal values. Thus, an effect of transport was shown for a distance of 100 km (P < 0.001). Many laboratories have established reliable reference values for β-endorphin, ACTH and cortisol values in the blood of healthy horses. Many factors, both endogenous and exogenous, affect hormone secretion and may lead to the misinterpretation of test results when values for individual animals are compared with reference values. In addition, slight variations could be ascribed to differences in techniques and some differences may also be explained by physical and psychological factors. The comparisons of results obtained in this study with published data reported for horses did not reveal any large discrepancies for circulating β-endorphin (8–26 pmol/l) [23,26-30], ACTH (3–7 pmol/l) [31,32] and cortisol (83–359 nmol/l) [2,31,33-35] levels. Any slight variation could be ascribed to differences in techniques. Transport conditions and handling of horses induced significant alterations in common physiological measures of stress, i.e. β-endorphin, ACTH and cortisol concentrations. Transportation of horses induced a very strong reaction of the adrenocortical system, attested during the preliminary phases by both β-endorphin and ACTH increases. Alleviating these stresses in transported animals should therefore be a prime concern for horse welfare and health. Transport is inevitably associated with a stress response but this can be avoided by adequate handling and management. Therefore, the use of hormonal stress markers merits consideration. The author(s) declare that they have no competing interests. EF was responsible for the study design, preparation and revision of the manuscript. PM was responsible for hormones and statistical analyses. VA carried out the blood sampling. LG was responsible for hormones analyses. AF was responsible for study design and manuscript preparation. All authors read and approved the final manuscript.   Source:


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